Semiconductor transistors, in particular field-effect controlled switching devices such as a Junction Field Effect Transistor (JFET), a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) and an Insulated Gate Bipolar Transistor (IGBT) have been used for various applications including but not limited to use as switches in power supplies and power converters, electric cars, air-conditioners, and even stereo systems. Due to structural efficiency and low on-resistance Ron, vertical trench MOSFETs are widely used, in particular in power applications.
Several semiconductor concepts use a sequence of thin trenches and semiconductor mesas or semiconductor lamellas. For example, one configuration of a vertical trench MOSFET is the so-called TEDFET (Trench Extended Drain Field-Effect Transistor) which allows for an improved decoupling of voltage blocking capability and on-resistance Ron compared to conventional MOSFETs by additionally controlling the conductivity in the drift region by a drift control region which is separated from the drift region by an accumulation dielectric formed in trenches vertically extending along the drift region.
Forming the deeply into the semiconductor material extending high quality accumulation dielectrics may, for example for power TEDFETS of higher blocking capability, become complex, in particular for semiconductor mesas and intervening trenches of higher aspect ratios and small pitch. Due the reduced mechanical stability of semiconductor mesas with high aspect ratio, the risk of deflecting the semiconductor mesas, for example during wet-chemical etching processes of rinsing and drying or due to a vibration, increases. Deflecting may result in adherence of neighboring semiconductor mesas, for example due to capillary forces. Furthermore, a thin mesa may even break off. These risks may be reduced by replacing water as solvent, for example by using isopropanol. However, this approach is not satisfactory for deep vertical trenches and deeply into the semiconductor material extending thin dielectrics, respectively. Using thicker mesas requires larger areas and thus increases costs.
Accordingly, there is a need to improve manufacturing methods for semiconductor devices having a plurality of semiconductor mesa.